A method for judging fatigue crack initiation of a multi-element complex air film hole single crystal blade

Abstract

The application belongs to the field of aero-engine design and is a kind of multi-element complex gas film hole single crystal blade fatigue crack initiation discrimination method. Firstly, the fracture characteristics of the test service blade are recorded to preliminarily judge the initiation position of the test service blade crack fracture. Then, according to the blade service load and manufacturing process data of the test service blade, a corresponding service fatigue damage simulation test piece is designed and manufactured, the service load of the test service blade is evaluated, the loading parameters are determined, and the service fatigue damage simulation test piece is loaded according to the loading parameters. The fracture characteristics after loading are matched with the test service blade, and the initiation position of the test service blade crack fracture is determined by judging the fracture characteristics of the corresponding service fatigue simulation test piece. The fatigue crack of the service blade can be truly simulated, and the performance changes of the remelt layer, diffusion layer, bonding layer, thermal barrier coating and the contribution to crack initiation can be intuitively verified.

Description

Technical Field

[0001] This application belongs to the field of aero-engine design, and specifically relates to a method for identifying the initiation of fatigue cracks in single-crystal blades with multi-component complex film-forming pores. Background Technology

[0002] To improve the thrust-to-weight ratio and turbine inlet temperature of aero-engines, several film cooling holes are often machined into the blade body of single-crystal turbines to reduce the actual operating temperature of the blade. However, the introduction of film cooling holes disrupts the integrity of the overall blade structure, causing the material around the holes to be under complex stress. In addition, the edge of the hole undergoes a high-temperature melting and cooling solidification process, during which a remelted layer of varying degrees is generated at the hole edge. The composition and structure of the remelted layer are significantly different from the single-crystal matrix and the complex micro-region structure resulting from the surface coating, equivalent to a complex multi-component system (matrix + diffusion layer + binder layer + thermal barrier coating). This severely affects the fatigue performance of single-crystal turbine blades, and accurately locating the initiation location of fatigue cracks in service blades is crucial for blade structure and process improvement.

[0003] Currently, the most commonly used method for identifying fatigue cracks in single-crystal film-supported perforated blades after service is to determine the location of crack initiation in the blade matrix solely through the analysis of fracture characteristics of the single-crystal matrix. This method rarely considers the potential performance changes and crack initiation contributions of the diffusion layer, bonding layer, and thermal barrier coating after a certain period of service, and lacks a precise method for identifying fatigue crack initiation in this complex multi-layered structure. Existing methods for opening the fracture surface of fatigue cracks in single-crystal blades with thermal barrier coatings include: (1) removing the non-conductive thermal barrier coating by sandblasting, and (2) opening the fracture surface using processing methods such as wire cutting. However, sandblasting not only causes significant plastic deformation at the crack location, resulting in secondary damage to the fracture surface, but also damages the coating on the blade surface, making it impossible to accurately locate the specific location of fatigue crack initiation.

[0004] Currently, there is no comprehensive and accurate method to determine the initiation of fatigue cracks in single-crystal blades with complex multi-layered film-forming pore structures after service. Summary of the Invention

[0005] The purpose of this application is to provide a method for identifying the initiation of fatigue cracks in single-crystal blades with multi-component complex film-forming pores, so as to solve the problem in the prior art that it is difficult to comprehensively and accurately identify fatigue cracks in single-crystal blades with multi-component complex film-forming pore structures after service.

[0006] The technical solution of this application is: a method for determining the initiation of fatigue cracks in a single-crystal blade with multi-element complex film-forming pores, comprising:

[0007] First, record the crack length, opening condition, and surface quality near the crack of the test blade. Then, sample the crack fracture surface of the test blade with thermal barrier coating, record the fracture characteristics of the test blade, and preliminarily determine the initiation location of the crack fracture surface of the test blade.

[0008] Obtain the service load and manufacturing process data of the test blades, and design and manufacture service fatigue damage simulation test pieces using the same methods;

[0009] Based on the preliminary assessment of the initiation location of the test blade, the service load of the test blade is evaluated, and the loading parameters of the service fatigue damage simulation test piece are further determined. The service fatigue damage simulation test piece is then loaded using a material testing machine according to the loading parameters of the service fatigue damage simulation test piece.

[0010] Fracture characteristics of service fatigue simulation test specimens are collected and correlated with fracture characteristics of test service blades. The initiation location of cracks in test service blades is determined by judging the fracture characteristics of the corresponding service fatigue simulation test specimens.

[0011] Preferably, after determining the initiation location of the crack fracture surface of the test blade, a corresponding service fatigue damage simulation test piece that has not been loaded is selected, and the same load is applied to the corresponding location of the crack fracture surface of the test blade on the service fatigue damage simulation test piece. It is then determined whether the fracture characteristics formed after loading are the same as the fracture characteristics of the test blade. If so, the verification is completed.

[0012] Preferably, after determining the initiation location of the crack fracture surface of the test blade, a corresponding service fatigue damage simulation test piece that has not been loaded is selected, and the same load is applied to the corresponding location of the crack fracture surface of the test blade on the service fatigue damage simulation test piece. It is then determined whether the fracture characteristics formed after loading are the same as the fracture characteristics of the test blade. If so, the verification is completed.

[0013] Preferably, the service fatigue damage simulation test piece structure includes a clamping part and a simulation work section; the clamping part is connected to a material testing machine, and the simulation work section includes a single crystal substrate and a coating; the single crystal substrate has film-forming holes, the size of which is completely consistent with the film-forming holes of the corresponding test service blade, and the casting process, heat treatment regime, crystal orientation and surface condition of the single crystal substrate are consistent with those of the corresponding test service blade; the coating is located on the underside of the single crystal substrate and includes a thermal barrier coating, an adhesive layer and a diffusion layer, and the spraying process and thickness of the thermal barrier coating, adhesive layer and diffusion layer are consistent with those of the corresponding test service blade.

[0014] Preferably, the method for sampling the fracture surface of the test blade is as follows:

[0015] ① In the longitudinal direction, cut the blade perpendicular to the crack direction at a distance of Q2-3mm from the crack endpoint using an abrasive wheel or diamond wire cutter, reaching a distance of P10-20mm from the crack endpoint in the longitudinal direction. ② In the transverse direction, cut parallel to the crack to a distance of 2-3mm beyond the other end of the crack. ③ Cut perpendicular to the crack direction to a distance of 10-20mm from the crack endpoint in the longitudinal direction. ④ In the transverse direction, cut parallel to the crack to a distance of 2-3mm beyond the other end of the crack. ⑤ Cut perpendicular to the crack direction to the intersection of ① and ②. In the thickness direction, according to the specific structure of the actual blade, use wire cutting to peel off the internal cracks layer by layer, controlling the peeling process to avoid damaging the internal free surface. In the longitudinal direction, tensile stress is applied to both sides of the crack to open the crack, and the fracture characteristics of the service single crystal blade are recorded using scanning electron microscopy combined with energy dispersive spectroscopy.

[0016] This application discloses a method for identifying fatigue crack initiation in single-crystal blades with complex multi-element film-forming pores. First, the fracture characteristics of a test blade in service are recorded to preliminarily determine the initiation location of the crack fracture surface. Then, based on the blade's service load and manufacturing process data, a corresponding service fatigue damage simulation test piece is designed and manufactured. The service load of the test blade is evaluated based on the preliminarily determined initiation location to determine the loading parameters of the service fatigue damage simulation test piece. The simulation test piece is then loaded according to these parameters. The fracture characteristics after loading are matched with those of the test blade in service, and the initiation location of the crack fracture surface is determined by analyzing the fracture characteristics of the corresponding service fatigue simulation test piece. This method can realistically simulate fatigue cracks in service blades and visually verify the performance changes of the remelted layer, diffusion layer, bonding layer, and thermal barrier coating, as well as their contribution to crack initiation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0018] Figure 1 This is a schematic diagram of the overall process of this application;

[0019] Figure 2 This is a schematic diagram of the sampling of the crack fracture surface of the blade tested in this application;

[0020] Figure 3 This is a schematic diagram of the overall structure of the service fatigue damage simulation test piece for this application;

[0021] Figure 4 for Figure 3 A partially enlarged structural diagram of section AA in the middle;

[0022] Figure 5 This is a schematic diagram of the method for identifying the initiation of fatigue cracks on the fracture surface of a single-crystal blade with multi-dimensional complex film pores after service, as described in this application.

[0023] 1. Clamping area; 2. Working section of the simulation part; 3. Air film pores; 4. Single crystal substrate; 5. Coating. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0025] A method for identifying fatigue crack initiation in single-crystal blades with complex multi-element film-forming pores, such as... Figure 1 As shown, it includes the following steps:

[0026] Step S100: Collect and test fracture characteristics of the service blades.

[0027] First, the cracks on the outer surface of the blades were observed using fluorescence non-destructive testing, optical microscopy, and scanning electron microscopy. Information such as crack length, opening condition, and surface quality near the cracks was recorded for the tested blades.

[0028] Then, the fracture surface of the service blade with thermal barrier coating was sampled and the fracture characteristics of the service blade were recorded.

[0029] Preferably, such as Figure 2 As shown, the method for sampling the fracture surface of the tested blade is as follows:

[0030] ① Cut the blade perpendicular to the crack direction at a distance of Q2-3mm from the crack endpoint using an abrasive wheel or diamond wire cutter, reaching a distance of P10-20mm from the crack endpoint in the longitudinal direction. ② Cut parallel to the crack in the transverse direction to 2-3mm beyond the other end of the crack. ③ Cut perpendicular to the crack direction to 10-20mm from the crack endpoint in the longitudinal direction. ④ Cut parallel to the crack in the transverse direction to 2-3mm beyond the other end of the crack. ⑤ Cut perpendicular to the crack direction to the intersection of ① and ②. During ③ and ⑤, control the cutting speed as much as possible when cutting near the crack to avoid secondary damage such as overheating of the crack fracture surface.

[0031] In the thickness direction, the internal cracks of the blade are peeled off layer by layer by wire cutting according to the specific structure of the actual blade. The peeling process is controlled to avoid damage to the free surfaces of the internal non-stiffening ribs, etc. Information such as the length of the internal crack, the opening condition, and the surface quality near the crack are also recorded. In the longitudinal direction, tensile stress is applied to both sides of the crack to open the crack. The fracture characteristics of the crack fracture surface matrix, remelting layer, diffusion layer, bonding layer, thermal barrier coating, etc. of the service single crystal blade are recorded using scanning electron microscopy combined with energy dispersive spectroscopy.

[0032] Based on the aforementioned sufficient fracture characteristics and existing experience, it is possible to make a relatively accurate preliminary judgment on the initiation location of the crack fracture surface of the tested blade.

[0033] Step S200: Design and manufacture service fatigue damage simulation test specimens.

[0034] Data such as blade service load and manufacturing process of the test blades can be obtained through the corresponding engine's BOM data.

[0035] The same methods described above were used to design and manufacture service fatigue damage simulation test pieces.

[0036] Preferably, such as Figure 3-4 As shown, the specific structure of the service fatigue damage simulation test piece includes:

[0037] Clamping part 1 connects to the material testing machine and is responsible for load transfer;

[0038] The simulated working section 2 is the part where the test target temperature and stress are applied, and the results are consistent with the simulation analysis of the temperature and load of the actual service blade damage area.

[0039] Simulation section working section 2 includes:

[0040] Single crystal substrate 4, this part is completely consistent with the actual service blade casting process, heat treatment system, crystal orientation, surface condition, etc.

[0041] Coating 5, which includes a surface thermal barrier coating, an adhesive layer, and a diffusion layer, ensures that the coating spraying process and thickness are completely consistent with the actual service blades.

[0042] The film gas hole 3 is located on the single crystal substrate 4. This part is completely consistent with the actual blade drilling process, the angle between the film gas hole and the wall at the damaged location, the hole shape, the hole diameter, the hole spacing, etc., and is responsible for realistically simulating the required service fatigue crack damage.

[0043] This service fatigue damage simulation test piece can simulate fatigue cracks in blades under various conditions, such as impact, low-cycle fatigue, high-cycle fatigue, and high-temperature fatigue.

[0044] This service fatigue damage simulation test piece takes into account all conditions of actual blade service, including temperature, load, complex micro-area structure, and manufacturing process. It can realistically simulate fatigue cracks in service blades and intuitively verify the performance changes of remelted layer, diffusion layer, adhesive layer, thermal barrier coating, etc., and their contribution to crack initiation.

[0045] Step S300: Load the service fatigue damage simulation test piece.

[0046] Based on the preliminary assessment of the initiation location of the test blade, the service load of the test blade is evaluated, and the loading parameters of the service fatigue damage simulation test piece are further determined, including test stress, temperature, time and other parameters.

[0047] The fatigue cracks of the service blade are simulated by loading the service fatigue damage simulation test piece with the loading parameters of the service fatigue damage simulation test piece using a material testing machine.

[0048] Since this type of fatigue crack is generated on a service fatigue damage simulation test piece, the initiation location of the crack fracture surface can be determined relatively directly and accurately, thereby obtaining the initiation location of the crack fracture surface of a test service blade with similar fatigue cracks.

[0049] Step S400: Determining the location of crack initiation

[0050] By collecting fracture characteristics of service fatigue simulation test pieces and correlating these fracture characteristics with those of the tested service blades, and by generating fatigue cracks in various service fatigue damage simulation test pieces, it is possible to find a fatigue crack that is basically similar to the tested service blade.

[0051] Design a method for identifying fatigue crack initiation in single-crystal blades with complex multi-element film-forming pores after service:

[0052] like Figure 5 As shown, fatigue crack initiation can be categorized into the following scenarios: ① Cracks initiate in the thermal barrier coating. When service blades and their simulated components are subjected to significant impact loads or prolonged high-temperature conditions, numerous microcracks perpendicular to the surface exist in the thermal barrier coating. These microcracks then propagate along the columnar crystal clusters of the ceramic layer, but do not extend to the bonding layer. ② Cracks initiate in the bonding layer. Under high-temperature, high-cycle fatigue conditions, cracks first appear in the bonding layer of service blades and their simulated components, then gradually propagate towards the substrate and thermal barrier coating. Substrate fatigue cracks initiate at the crack ends in the bonding layer and propagate along the slip surface. ③ Cracks initiate in the diffusion layer. Crack initiation in this area is mainly due to the unstable microstructure (SR) formed by the interdiffusion between the bonding layer and the substrate during service. Caused by Z, the fracture characteristics are manifested as initiation and propagation along the TCP brittle phase interface; ④ Cracks initiate in the remelted layer. Due to problems such as the control of EDM drilling process parameters and the small angle between the gas film pore and the wall, the remelted layer in the sharp corner area is thick and the cooling effect is poor, resulting in the initial crack. Under the action of service vibration stress, it further propagates. The fracture characteristics show that there are steps and interfaces in the source region. There are obvious differences in the fracture characteristics and energy spectrum results on both sides of the interface. The source region mainly has granular morphology characteristics and local fine secondary cracks; ⑤ Cracks initiate in the matrix. The source region has slip cutting γ' phase characteristics, accompanied by river patterns, fatigue bands, radial ridges and other morphologies. The specific location of the matrix initiation can be determined from its convergence direction.

[0053] By identifying the five types of crack characteristics mentioned above, it is possible to accurately determine the specific type of crack and where it originates, thereby identifying the initiation location of the crack fracture surface on the corresponding tested blade.

[0054] After determining the initiation location of the crack fracture surface on the test blade, a corresponding unloaded service fatigue damage simulation test piece is selected. The same load is applied to the corresponding location of the crack fracture surface on the service blade, and it is determined whether the fracture characteristics formed after loading are the same as those of the test blade. If so, the verification is complete; otherwise, the fracture characteristic is re-tested and verified until the fracture characteristics are identical. Through this verification, the initiation location of the crack fracture surface on the test blade is further determined.

[0055] This application first records the fracture characteristics of the test blade in service to preliminarily determine the initiation location of the crack fracture surface. Then, based on the blade service load and manufacturing process data of the test blade in service, a corresponding service fatigue damage simulation test piece is designed and manufactured. Based on the preliminarily determined initiation location of the test blade in service, the service load of the test blade in service is evaluated to determine the loading parameters of the service fatigue damage simulation test piece. The service fatigue damage simulation test piece is then loaded according to these loading parameters. The fracture characteristics after loading are matched with those of the test blade in service. By judging the fracture characteristics of the corresponding service fatigue simulation test piece, the initiation location of the crack fracture surface of the test blade in service is determined.

[0056] In this way, regardless of the material's service life or the performance changes of the coating, as long as the corresponding fracture characteristics are simulated, the initiation location of the crack fracture can be determined by first identifying the service fatigue simulation test piece that considers all conditions of the tested blade, including service temperature, load, complex micro-region structure, and manufacturing process. Simultaneously, it can realistically simulate fatigue cracks in service blades and visually verify the performance changes of the remelted layer, diffusion layer, adhesive layer, and thermal barrier coating, as well as their contribution to crack initiation.

[0057] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for identifying the initiation of fatigue cracks in a single-crystal blade with multi-element complex film-forming pores, characterized in that, The application relates to a method for determining the crack initiation position of a test service blade. The crack length, opening condition and surface quality near the crack of the test service blade are recorded, the crack fracture of the service blade with a thermal barrier coating is sampled, the fracture characteristics of the test service blade are recorded, and the crack initiation position of the test service blade is preliminarily judged; The service load and manufacturing process data of the test service blade are obtained, the service fatigue damage simulation test piece is designed and manufactured according to the same method, the service load of the test service blade is evaluated according to the preliminarily judged crack initiation position, the loading parameters of the service fatigue damage simulation test piece are further determined, the service fatigue damage simulation test piece is loaded by a material testing machine according to the loading parameters of the service fatigue damage simulation test piece, the fracture characteristics of the service fatigue simulation test piece are collected, the fracture characteristics are associated with the fracture characteristics of the test service blade, and the crack initiation position of the test service blade is determined by judging the fracture characteristics of the corresponding service fatigue simulation test piece. After the crack initiation position of the test service blade is determined, the corresponding service fatigue damage simulation test piece which is not loaded is selected, the same load is applied to the corresponding position of the service fatigue damage simulation test piece corresponding to the crack initiation position of the test service blade, and it is judged whether the fracture characteristics formed after the loading are the same as the fracture characteristics of the test service blade. The method for judging the fracture characteristics of the service fatigue simulation test piece is as follows:

2. The method of claim 1, wherein the method is a method of determining the fatigue crack initiation of a multi-element complex airfoil single crystal blade, characterized by: when there are microcracks in the thermal barrier coating which are perpendicular to the surface of the thermal barrier coating and the microcracks expand along the ceramic layer columnar crystal clusters but do not expand to the bonding layer, it is judged that the crack is initiated in the thermal barrier coating; 3. The method for determining the initiation of fatigue cracks in a single-crystal blade with multi-element complex film-forming pores as described in claim 1, characterized in that, when there are cracks in the bonding layer and the cracks expand to the substrate and the thermal barrier coating, the substrate fatigue crack is initiated at the end of the bonding layer crack and expands along the slip surface, it is judged that the crack is initiated in the bonding layer; when the crack is at the TCP brittle phase interface and expands, it is judged that the crack is initiated in the diffusion layer; when there are steps and interfaces in the crack source area, the fracture characteristics and energy spectrum results on both sides of the interface are different, the source area has a granular morphology, and there are small secondary cracks in the local area, it is judged that the crack is initiated in the remelted layer; when the crack has the slip cutting gamma prime phase characteristics, is accompanied by river pattern, fatigue strip and radiation ridge line morphology, it is judged that the crack is initiated in the substrate. The structure of the service fatigue damage simulation test piece comprises a clamping part (1) and a simulation piece working section (2); the clamping part (1) is connected with a material testing machine; the simulation piece working section (2) comprises a single crystal substrate (4) and a coating (5); the single crystal substrate (4) is provided with an air film hole (3); the air film hole (3) is completely consistent in size with the air film hole (3) of the corresponding test service blade; the single crystal substrate (4) is consistent with the corresponding test service blade in casting process, heat treatment system, crystal orientation and surface state; the coating (5) is arranged on the lower side of the single crystal substrate (4) and comprises a thermal barrier coating, a bonding layer and a diffusion layer; the spraying process and thickness of the thermal barrier coating, the bonding layer and the diffusion layer are consistent with those of the corresponding test service blade. ​ 4. The method of claim 1, wherein the method is a method of determining the fatigue crack initiation of a multi-element complex airfoil hole single crystal blade, characterized by: ​ 5. The method of claim 1, wherein the method is characterized by: The fracture sampling method of the test service blade is: (1) 2-3 mm away from the crack end point Q in the longitudinal direction, the blade is cut along the vertical crack direction by using a grinding wheel and a diamond wire cutting machine, and reaches 10-20 mm away from the crack in the longitudinal direction P; (2) cutting parallel to the crack in the transverse direction to 2-3 mm beyond the other end point of the crack; (3) cutting perpendicular to the crack direction to 10-20 mm away from the crack in the longitudinal direction; (4) cutting parallel to the crack in the transverse direction to 2-3 mm beyond the other end point of the crack; (5) cutting perpendicular to the crack direction to the intersection point of (1) and (2); according to the actual structure of the blade, the internal crack of the blade is peeled off layer by layer by using wire cutting in the thickness direction, and the peeling process is controlled to avoid damaging the internal free surface; the crack is opened by using tensile stress on both sides of the crack in the longitudinal direction, and the fracture characteristics of the service single crystal blade are recorded by using a scanning electron microscope combined with energy spectrum analysis.

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